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diff rust/hg-cpython/src/dagops.rs @ 51252:24d3298189d7
rust-index: document safety invariants being upheld for every `unsafe` block
We've added a lot of `unsafe` code that shares Rust structs with Python.
While this is unfortunate, it is also unavoidable, so let's at least
systematically explain why each call to `unsafe` is sound.
If any of the unsafe code ends up being wrong (because everyone screws up
at some point), this change at least continues the unspoken rule of always
explaining the need for `unsafe`, so we at least get a chance to think.
| author | Rapha?l Gom?s <rgomes@octobus.net> |
|---|---|
| date | Thu, 23 Nov 2023 03:41:58 +0100 |
| parents | 578c049f0408 |
| children |
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--- a/rust/hg-cpython/src/dagops.rs Sun Oct 29 12:18:03 2023 +0100 +++ b/rust/hg-cpython/src/dagops.rs Thu Nov 23 03:41:58 2023 +0100 @@ -28,6 +28,7 @@ revs: PyObject, ) -> PyResult<HashSet<PyRevision>> { let py_leaked = py_rust_index_to_graph(py, index)?; + // Safety: we don't leak the "faked" reference out of `UnsafePyLeaked` let index = &*unsafe { py_leaked.try_borrow(py)? }; let mut as_set: HashSet<Revision> = rev_pyiter_collect(py, &revs, index)?; dagops::retain_heads(index, &mut as_set)